Two-way repeater



Feb. 7, 1928.

J. s. JA'MMER ET AL TWO-WAY RE'EEATER Filed Jun e so. 1924 2 Sheets-Sheet 1 We sr .STahon hymn/v: (/0409 J. c/0/77/776/ MW/eJWWee/Y W MAW Feb. 7,

J. S. JAMMER ET AL TWO-WAY REPEATER File June 50, 1924 2 Sheets-Sheet 2 Fatented Feb. 7, 1928.

UN TED srarss JACOB S. JAMMER, F NEW YORK, N. '55., AND CHARLES W'. GREEN, D1 MILLBURQL NEW JERSEY, ASSIGHORS TO WESTERN-ELECTRIC COMPANY, INCORPORATED, -01 NEWYYORK, N. Y., A CORPORATION OF NEW YC'RK.

, TWO-WAY REPEATER.

Application field time so, 1924'. Serial No. 723,165.

This invention relatesto two-way amphtying repeaters adapted for use in multiplex carrier current signaling systems.

in object of the invention is to produce an efficient and economical two-way repeater.

A related object ofthe invention is to increase the gain and level of a two-way amplit'ying repeater.

Repeaters .of this type are employed in multiplex carrier current telephone and tele graph systems operated on a group ire quency basis wherein the different channel frequencies. for transmissionin one direction are grouped in a different frequency range from that employed for transmission in thelopposite-direction.

The'attenuation of currents of carrier frequencies resulting through their transmis sion over long distance lines is much greater than those of voice frequency, and the successful operation of carrier systems has hcretotore depended on the use otrepeaters at comparatively frequent intervals on the line. The number of repeater points required in such a systeminay be reduced by increasing the amplification or gain ot'the individ .ual repeater amplifiers, which are usually of the three-element vacuum tube type. How ever, merely increasing the amplification in repeater circuits of the types heretofore known, beyond a'certain load limit, olfers no advantage, since as the load is increased, tubes of greater load capacity are required with consequently greater initial cost and greater maintenance costs.

This invention reduces the number of repeater points in a commercial carrier current signaling system while at the same time actually reducing the number of amplifiers employed in the system so that a large geographical distanceis spanned with a greater v economy of apparatus than has heretofore been thought possible.

According to afeatureof the invention the gain and level of a repeater are materially increased by arranging the amplifying structures in a novel manner to give increased economy and efficiency of operation. A common amplifier is provided for the two groups of frequencies for one stage of amplification, and individual amplifiers are provided for each group for another stage of amplification; Each amplifier, may be utilized to its full capacity, the second stage amplifiers operating at a. higher level than the first stage amplifiers. suitably dividing the load between the individual amplifiers and the common amplifier for the two frequency groups, the same gain can be obtained with thesame quality of transmission but with a smaller number of amplifiers.

vention "W111 be described asapplied The i to a norm-pier; tem, although may ap L91 :3.

The invention modifications ve tieular type of carepeater is to be employed. certain modifications. for example, may be particularly adapted for use in the Well-known carrier telephone suppression system, that is, the system in which the nnmodulated carrier rier current telephone sys- F/rll be understood that it led to bther signaling syssusceptible of various are suited to the parcomponent is not transmitted, While other modifications are especially suited for use in'earrier telephone systems in which the unmodulated carrier component is transmit ted along with side hand components.

The various features and advantages of the invention will appear-from the following description and the accompanying drawings in which:

Fig. l is a diagrammatic view illustrating a terminal station of a carrier suppression telephone system. 4

rier system in which the t Fig. 2 isa diagrammatic view of a carrier station and a mid-line repeater of a carrier telephone system interconnected by the multiplex line ML. 1 l

The usual east terminal station, which isidentical to the west terminal station shown. in Fig; 1, is omitted for the sake of simplicity in the description.

The terminal apparatus at the west sta telephone repeater station embodying the tion comprises a plurality of transmitting channels TC TC and TC,, connected through a common transmitting circuit TL Carrier currents are utilized for transmission over the line ML and are grouped as to their frequencies, the higher frequencies. as a group, being used for transmission from west to east, and the lower frequencies, as a group, being used for transmission from east to west.

I A high pass grouping filter HP is paired with a low pass grouping filter LP at the terminal stations. These filters serve to sep arate the directional groups of carrier waves to the respective terminal transmitting and receiving circuits. These filters andeach ot the other filters shown throughout the sys tem may be designed in accordance with the principles set forth in the United fitat es patent to Campbell, No. 1,227,113, issued May 22, 1917. Specific types of both high and low pass filters are shown for example in Fig. 11 of the Campbell patent.

Low frequency lines L L and L,, which may be telephone lines or other types of signaling lines, are associated with channels TC RC T C 'RC and TC RC re spectively, for simultaneous and independent communication over the line ML with corresponding similar lines-at the east station (not shown). I

' The low frequency lines are provided with balancing artificial lines or networks N N dmd N respectively, and with differential repeating coils H H and H com- 40 monly known as hybrid coils for enabling independent transmission in the two directions between the line and the hightreqnency terminal apparatus.

Transmitting channel TC includes a modulator M, and,a band filter TBF Similarly, transmitting channel TC includes a modulator M and a band filter TBF while channel TC, includes a modulator M and" Receiving channelltC, includes a demodulator D and a band filter RBF Simi- "larly, channel RC includes a demodulator D and a hand filter RBF while channel RC, includes a den'iodulator D and a hand filter RBF The modulators associated with the various transmitting channels throughout the system are of the balanced type disclosed in the U. S. patent to Carson, No. 1,343,306, issued June 15', 1920, designed to suppress the unmodulated carrier from transmission. The various demodulators may he of the well-known vacuum tube detector type shown in Fig. 49 of an article entitled Carrier current telephony and telegraphy? by Messrs. Colpitts and Blackwell published in the. Proceedings of the American Institute of Electrical Engineers, 'vol. 40, 1921.

The carrier system outlined above is, as*

lated waves of this character, it is necessary that the carrier wave supplied to the de modulator at the receiver be of substantially the same frequency as the carrier wave which was suppressed at the transmitter. A system of this general character, is described in connection with ,Fig. l9 of the Colpitts and Blackwell article, supra. I

Carrier currents of the frequency assigned to ch anI el'llC are'supplied from a source TO, to the modulator M wherein they are modulated by voice frequency currents of othersignaling currents from the low irequency L Carrier sources T0 and T0,, are similarly.associated with modulators M and M respectively, while carrier current sources R0,, R0 and R0,, are associated with demodulators D D and 1),, respectively.

As noted'above. the carrier current sources R0 R0 and R0 are necessary to supply to the incoming side bands in each receiving channel 'the carrier current which was sup;

pressed at the transmitting end 01 the cha'nnel.

The various band filters associated with the terminal transmitting and receiving channels are-so designed that they 'will transmit one of theside bands, either the upper or lower as desired, produced by modulation in the respective'channels, and will suppress from transmission frequencies lying outside of such band. 7

{Voice frequency currents originating, for instance, in the low frequency line L at the west station pass through the associated hybrid coil H into the modulator M in the transmitting channel TC,. There is likewise i'ed into the modulator the carrier current from the oscillator 0,, as described above.

Of the components of modulation appeal-inc are thence transmitted tothe respectiveretezsssss ceiving channels.

Currents incoming-at the 'west stationpass' through the low pass grouping filter LP transmission line sections 8V and E. This repeater provides two stages of amplification in which a common amplifier is employed for the two groups of frequencies for the first stage of amplification, and individual amplifiers are employed for each group for the second stage of amplification.

As pointed out above, the currents transmitted from the west station, which are impressed upon the repeater from linesection V, are comprised in a higher frequency group than those transmitted .from the east station which are impressed upon the repeater from line section E.-

The repeater consists of upper and lower repeater branches, which includeone-way selective paths for each of the frequency Y amplifiers areemployed in each of the paths These selective paths include frequency discriminating filters which direct the incoming currents through the proper repeater channels. One amplifier. is employed common to both of the selective paths for one stage of amplification and separate for the second stage of amplification;

The upper branch of the. repeater includes a high pass input filter HPIF designed to pass frequencies of the upper group trans- 'mitted from west to east, and a low pass input filter LPIF. designed to pass frequentries of the lower group transmitted from east to, west. 1

A common amplifier CA has its input circuit coupled by means of a transformer 5 to the-upper branch of the repeater at a pointintermediate the high pass input filter HPIF and thelow pass input filter LPIF. The output circuit of amplifier CA is coupled to the lower branch of the repeater by means of a transformer 6. The amplifier CA comprises two vacuum tubes of the three-element electron discharge type arranged in a so-called push-pull circuit so'that distortion is practically eliminated. The principles of the push-pull type of cir-' 'cuit discussed at length in the United States latent to l-lartley, No. 1,494,905, issued May 520, 1924i. p

in receiving channel RC are. put and The lower branch ofthc repeater contains an amplifier WA for amplifying currents transmitted from west -to east, and an amplifier'EA for amplifying currents trans. niitted. from east to west. In order to provide proper frequency separation between the upper group of frequencies to be transmitted through amplifier lVA and the lower group of frequencies to be transmitted through the amplifier EA, a" high pass rouping filter HPGF andfa high pass output filter HPOF are associated with the i11 output circuits of the amplifier .VVA, and and. a low pass output filter LPOF are similarlyassociated with the input and output circuits of the amplifier EA. I

It will be seen from the above that the repeater shown in Fig. 2 includes one-wayv selective paths. for'each of the frequency groups. Currents incoi'ning from the line section 'lV pass through the high pass input filter HPIF and are amplified inthe common'ainplificr CA. Currents of this par ticular group of frequencies appearing in the output of the amplifier CA are selec tively passed through the high pass grouping filter HPGF to the west to east amplifier \VA, and thence through the high pass output filter'HPOFto the line section E. The currents comprised in the lower group of frequencies incoming fromthe linev E pass through the low pass input filter LPIF and are likewise amplified in the common amplifier CA. These currents are selec tively passed through the low pass grouping filter LPGF to the east to west amplifier EA, whence they are transmitted through the low pass output filter LPOF to the line section-W.

The electrical and economical advantage of the above-described amplifier may be'secn from a consideration of the curves of Fig. 4-, in which energy level is plotted against distance. r,

The curve A of Fig. 4 represents the ena low pass grouping filter LPGF orgy levels at which it has heretofore been v possible to transinit currents between terminal stations W and E, while curve B represents the energy. levels at which it is possible to transmitthe currents between the same terminal stations in accordance with this invention. In both cases, the fig ures herein given are representative of a three-channel carrier telephone suppression system of the type described above, stations lV and E being identical to the terminal station shown in Fig. 1. While these curves illustrate transmissions from station W to station E the same conditions apply to transmissions in the opposite direction.

It is customaryv in carrier current telephone practice to speak of the energy levels at which the carrier currents are transmitted in terms of miles of standard cable over which the currents are transmitted at' 800 cycles per second. The formula for miles, gain or loss, as the case may be, may be represented as follows:

M=2-L12 log where 1, represents the input current on the line, and 2 represents the output on the line. For practical purposes ity is customary to lesi mate a point on the vertical scale oi Fig. i as the Zero level or zero miles gain from which the remainder of the scale may be calibrated. The point on the scale of Fig. l corresponding to Zero miles represents an energy level of -l mils in a 600 ohm circuit, or .01 watt, for a single channel system. For a three-channel system such as that herein described, however, Zero miles represents an energy level of 6.8 mils in a circuit of similar impedance.

In three-channel carrier telephone systems it has been customary to impress the currents -upon the transmission line at a level of plus 10 miles, or about 20 mils, as shown by the curve'A, which shows the energy level at which the carrier currents are impressed upon the line at station W. As shown by the curve A, there is a considerable loss in energy caused by the attenua tion of the carrier currents as they are transmitted over the main line. At a point 150 geographical miles from station W. the energy level has been reduced to -30 miles,

or about .25 mils. At this point it becomes necessary to insert an amplifying repeater on the line since any further substantial loss would reduce the carrier currents to the noise level on the line. The repeater R, is, therefore, inserted to raise the level of the carrier currents back to plus 10 miles, or about 20 mils. It will readily be seen, therefore, that due to the attenuation of the carrier currents two repeaters R R must be inserted between terminal stations W and E on a line 450 miles in length.

In accordance with the invention the carrier currents may be transmitted over the system at high energy levels with a greater economy of apparatus than has heretofore been thought practicable. The carrier currents may be impressed upon the line at a terminal station, for example at station lV,

line. The carrier currents transmitted from station V in passing through the common amplifier CA are raised to an energy level of plus 10 miles indicated by the line a, Without overloading this amplifier, and are then further raised from an energ I level of plus 10 miles to an energy level of 30 miles indicated by line Y, in the amplifier WA, which amplifier operates at higher energy levels than the amplifier CA. This amp ifier, for example, and also amplifier EA, may consist of larger tubes than those employed in the amplifier CA of this figure. At the same time, carrier currents transmitted from station E to station V] are amplified in the common amplifier CA and in the east to west amplifier EA at the repeater point R The above-described arrangement provides a. repeater which may be economically manufactured and maintained. In the sup-' pression type carrier system which is illustrated in the drawings the load on the common amplifier CA would never be greater than the total number of one-way channels, because while it is possible to transmit in both directions, the parties at the ends ot a circuit do not talk simultaneously.-

The repeater illustratedin Fig. 2 is also adapted for use in carrier telephone systems in which the carrier is continuously transmitted throughout the system. A system of this general type is described in connection with Fig. 42 of the Colpitts and Blackwell article, supra. In .such a system, the carrier currents transmitted in both directions, to gether with their upper or lower side bands, are amplified in the common amplifier CA,

which operates from the relatively low in coming level, and can therefore be of relatively small load capacity. For the second stage 01 amplification, the directional groups of carrier currents divide, the higher group of frequencies being transmitted through amplifier WA and the lower group of frequenciesbeing transmittedthrough the amplifier, EA. These two amplifiers operate from the output level of amplifier CA and are of correspondingly greater load capacity.

Fig. 3- shows a modification of the repeater of Fig. 2 in which individual amplifiers are employed for the upper and lower groups of frequencies for the first stage of amplification and a common high power amplifier is employed for the two groups for the second stage of amplification. This repeater is best adapted for use in systems in which the uumodulated carrier component is suppressed. 'The currents comprised in the upper trequcncy group incoming over the line section lV are transmitted through the high pass in put filter HPIF, west to east amplifier lVA, high pass grouping filter HPGF, common amplifier CA, high pass output filter HPOF to line section E. The currents comprised in the lower frequency group in-- coin ng from line section E pass through the low pass input filter LPIF, the east to west amplifier EA, low pass grouping filter LPGF, common amplifier CA, low pass output filter LPOF to line section W.

loo

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.plifier and two filters are The curve of Fi 4 which 'Was used to illustrate the operating levelof the repeater of Fig. 2 is equally applicable to the repeater of In the case of the repeater of Fig. 3, referring particularly to west to east transmissions, the west to east amplifier MA at repeater point It, raises the level of the currents transmitted therethrough from 3() miles to plus 10 miles indicated bythe line X, while the common amplifier CA raises the currents transmitted therethrough from a level of plus 10 miles to a level of plus 30 miles, indicated at Y.

In this type of system to whichthis repeater is particularly suited, as has been explained in detail above, the carrier and one side band is suppressed and only the relatively small upper or lower side bands are transmitted. F or this reason therejis only a very small load on the amplifiers WA and EA, this load at no time being greater than Y the total number of oneway channels since, as pointed out above, the operators at the ends of a circuit do not talk simultaneously.

The common amplifier CA is designed to pcrate at a higher level than the amplifiers \VA and EA, the input currents applied to thiscoinmon amplifier being at a level of plus miles, and the gain introducedby the amplifier raising the level of these currents to plus miles.

Aside tromthe economical advantages of the invention, it will be seen that the total amplification and total filter discrimination of the repeaters of Figs.2 and 3 are broken up nto successive alternate gains and losses,

to that the absolute gain or loss in anyone unit is smaller than required in the usual repeater arrangement in which a single amemployed in each direction.

The invention set forth herein is, of course, susceptible of various other modifications and adaptations. The figures given herein are also to be taken as merely illustrative of the invention and are not to be considered as limiting its scope in any way.

What is claimed is: 1

1. in a two-way repeater for wave trans mission systems comprising line sections for two-way transmission in which the waves transmitted in opposite directions are co1n prised in ditt'erent frequency groups, a oneway selective path interconnecting said line sections for one of said. frequency groups, an other one-way selective path interconnecting said line sections for the other of said frequency groups, an amplifier common to both said paths-and separate amplifiers in each of said paths.

:2. In a two-way repeater mission systems comprising line sections for two-way transmission in which the waves transmitted in opposite directions are comnected between said for wave trans two-way transmission inwhich the waves transmitted in opposite directions are comprised in different frequency groups, an iiiput and an output repeater branch. eoniiected to each line section, an amplifier coninput and output branches for amplifying wares comprised in both frequency groups, and separate am-' pliliers for each ot' said frequency groups in said output branch.

at. In a carrier wave signaling system in which the oppositely directed waves are comprised in different frequency groups, two line sections, a two-way repeater having input and output branches connected to each of said line sections, a "common ani-.

plifier for all of said waves connected between said branches, grouping filters in each of said branches, and amplifiers in said out put branch between the. output of said coninion amplifier and each of said line sections.

5. In a carrier wave signaling system in which the oppositely directed waves are line sections, a two-way repeater put and output branches connected to each of said line sections, a common amplifier for all of said 'waves connected between said branches, grouping filters in said input repeater branch, and amplifier units comprising two wave filter sections joinedby an amplifier disposed in said output repeater branch between the output of said common amplifier and each of said line sections.

comprised indifferent frequency groups, two I ha-wng inlOO '6. A repeater system for through repeating between two two-way transmission lines comprising a pair of oppositely directed oneway transmission branches connected to each line, a common one-way path connected between the incoming and the outgoing branches, a common amplifier in said come men path and other amplifiers in certain of said branches, said "amplifiers in said branches operating in tandem with the aniplifier in the common path and adding their respective amplifications to that of. said common amplifierwhereby the added gain of each one-way branch over that furnished ize by the common amplifier is determined by the amplifier individual to the branch.

In witness whereof, we hereunto subscribe our names this 16th day of June A. D., 1924-.

- JACOB S. JAAHIER CHAR-LES W. GREEN. 

